(1) Field of the Invention
This invention relates to a multi-layer plastic drawn and molded container excellent in transparency, rigidity, mechanical strength, water resistance and gas barrier property to oxygen and the like and having a practically satisfactory interlaminar peel strength under falling, shaking or impact, and to a process for the preparation of this excellent container.
(2) Description of the Prior Arts
It is well known that when a thermoplastic resin is drawn at a relatively low temperature, namely at a temperature lower than the melting point or softening point of the resin or a temperature just above the melting point or softening point of the resin, as a result of orientation of the polymer chain or crystal, such properties as rigidity, mechanical strength, gas barrier property and transparency can be improved. These improvements are practically utilized in biaxially drawn films, filaments, drawn tapes, biaxially drawn blow bottles and draw-molded cups.
In the field of narrow- and broad-mounted hollow plastic containers, for example, a biaxially drawn blow bottle of the vinylidene chloride resin type molded according to the method disclosed in Japanese Patent Publication No. 8583/63 has heretofore been broadly used as a ketchup bottle because it has an excellent gas barrier property. However, because of generation of poisonous gases on burning or migration of the monomer or additive into the content, bottles of this type are hardly used at the present. Biaxially drawn blow bottles of polypropylene formed according to the principle, method and apparatus disclosed in Japanese Patent Publication No. 16245/63, Japanese Patent Application Laid-Open Specification No. 3492/71, etc., have excellent transparency, rigidity and mechanical strength, and they are broadly used as bottles for shampoo or the like instead of polyvinyl chloride bottles in U.S.A. and as bottles for medicines, for example, Ringer's solution, instead of glass bottles in Japan. Further, broad-mouthed polypropylene cups prepared by solid-phase pressure forming at a relatively low temperature according to the method disclosed in Kunststoffe Bd. 65, 1975, H. 10, page 666 have now been attracting attentions as substitutes for polyvinyl chloride cups. Further, biaxially drawn blow bottles of polyethylene terephthalate disclosed in the specification of U.S. Pat. No. 3,733,309 have been test-marketed as bottles for carbonated drinks and now attract attentions in the art.
In case of the above-mentioned biaxially drawn blow bottles of the vinylidene chloride resin type, when a contained liquid, semi-liquid or pasty food has contact with the inner wall of the bottom, a problem of migration of the monomer or the like rises, and they cannot be regarded as practical semi-rigid containers. Biaxially drawn blow bottles of polypropylene and polypropylene cups prepared by solid phase pressure forming are inferior in the gas barrier property, and they cannot substantially be applied to foods of which the preservability is sensitive to oxygen permeating through the container wall. Although biaxially drawn blow bottles of polyethylene terephthalate have a relatively high gas barrier property and are very excellent in rigidity and transparency, when they are allowed to stand in an atmosphere maintained at 60.degree. to 70.degree. C. for 3 to 5 minutes, they show such thermal shrinkage as an empty volume shrinkage of 1 to 3%, a total height shrinkage of 0.4 to 0.8% and a barrel diameter shrinkage of 0.7 to 1.2%. Further, when they are allowed to stand in an atmosphere maintained at 80.degree. C. for 1 minute, they are deformed to such an extent that they cannot be practically used. Accordingly, these bottles cannot be used when hot filling of contents is conducted or for storage of foods requiring heat sterilization, for example, sauces.
For the foregoing reasons, as in case of melt-molded containers, multi-layer structures in which defects of respective resins are compensated and which can meet practical demands are required in case of not only biaxially drawn blow molded containers prepared by forming a thermoplastic resin into a bottomed or bottomless parison and conducting the step of elongating the parison in the axial direction thereof at a relatively low temperature, for example, the melting point of the resin and the step of inflating the parison in a direction rectangular to the axial direction simultaneously or in this order (namely in sequence) but also biaxially drawn cups pressure-formed in the solid phase from a sheet at a relatively low temperature.
Drawn multi-layer containers are proposed in, for example, the specification of U.S. Pat. No. 3,733,309 and Japanese Patent Application Laid-Open Specification No. 32164/73, but these known drawn multi-layer containers are still insufficient from the practical viewpoint with respect to the interlaminar strength between every two adjacent layers, selection of consituent resin layers and selection of molding conditions such as the molding temperature and draw ratio. In addition, use of an unsaturated carboxylic acid-grafted thermoplastic resin as an adhesive improving the interlaminar peel strength has been proposed in, for example, Japanese Patent Application Laid-Open Specification No. 67384/76, but in this proposal, no sufficient regard is paid to the relation between the molding conditions such as the molding temperature and draw ratio and the adhesiveness.